Tectonic implications of transpression and transtension: Upper Rhine Graben

[1] Seismic reflection data from the Upper Rhine Graben (URG) show a series of synclines along the linear eastern boundary faults from north of Karlsruhe to the Jura Mountains. Similar structures do not characterize the northern segment of the graben. The synclinal shape is portrayed by inversion related to transpression on the linear boundary faults, coupled with the conserved easterly dip of the sediments farther inside the tilted hanging block. The onset of transpression preceded the known early Burdigalian unconformity but was also an early Miocene event. It suggests that the regional compression axis (σ1) in early Miocene had a trend between 315° and 0°. The continuous transtension in the northern segment suggests that at no time during the history of the URG was the regional σ1 horizontal with a NE-SW trend. The lack of transpressional structures in the younger Plio-Pleistocene sediments along the entire eastern boundary of the URG suggests a late change in the regional stress field. The main eastern boundary faults and synclines north and south of Baden-Baden are all continuous and have the same trend. Kinematically, they form a single graben segment and respond to the regional stress in the same way.